Network firewall / mySQL

Hi all -

This question is regarding outbound firewall for a droplet. Here is droplet configuration:

• Node server 16.4.0 running behind Nginx
• App running nestJS/typeorm connecting to mySQL DB on AWS RDS

When trying to open the connection to mySQL DB, get the following error in the logs:

Error: connect ETIMEDOUT
    at PoolConnection._handleTimeoutError (/var/www/html/node_modules/mysql2/lib/connection.js:189:17)
    at listOnTimeout (node:internal/timers:559:17)
    at processTimers (node:internal/timers:502:7) {
  errorno: 'ETIMEDOUT',
  code: 'ETIMEDOUT',
  syscall: 'connect',
  fatal: true
}

In DO networking firewalls, if we add UDP ports to outbound rules, then the connection establishes successfully.

Just wondering if there is any explanation to this behavior, i.e. why the need to add UDP for outbound ports as mySQL operates over a TCP port normally.

Any thoughts would be appreciated.

Thanks!